Project Summary/Abstract The overarching goals of this proposal are to contribute to the understanding of the causes, mechanisms, and potential strategies for prevention of the international epidemic of chronic kidney disease of unknown origin (CKDu). Our central hypothesis is that CKDu results from the combined effects of dehydration and exposure to nephrotoxins, due to enhanced reabsorption of nephrotoxins into the renal tubules during periods of recurrent dehydration. Access to a large population of sugarcane workers in cooperation with a major Guatemalan agribusiness will allow for a study that characterizes and determines the contribution of occupational and environmental risk factors and that also evaluates subclinical kidney responses using biomarkers of early biological change in CKDu. This research will: a) identify occupational, environmental, and lifestyle factors that place agricultural workers at risk for the development of CKDu by conducting robust environmental and biological exposure assessments and b) examine underlying mechanisms by which dehydration contributes to increased risk of CKDu in conjunction with nephrotoxic exposures. To address this hypothesis, two aims are proposed: Aim 1 focuses on identifying sources of nephrotoxic exposure and risk factors for renal damage in Guatemalan sugarcane workers, using prospective, quantitative environmental and biological exposure assessments. Aim 2 will evaluate biomarkers of effect, including neutrophil gelatinase-associated lipocalin (NGAL) and copeptin as markers of early biological change, in order to identify workers with increased risk of worsening renal function. The proposed study is both case-control and prospective cohort in design. First, it will collect baseline questionnaire and clinical data and biological samples from individuals with either reduced kidney function (n=75) or normal kidney function (n=100) applying for field work employment at a sugarcane plantation in southwest Guatemala. In addition, individuals who have normal kidney function at the time of hire (n=100), will be monitored using repeat measurements at two additional time points spanning the 6-month sugarcane harvest. At these two time points, dehydration and heat stress, recognized risk factors, will also be measured in the workers. Within- and between-worker variation and magnitude of change will be assessed for selected urinary and blood biomarkers across the harvest. As a result of prior research, the specific nephrotoxic exposures to be evaluated will include non-steroidal anti- inflammatory medication use (diclofenac), tobacco use (cotinine), selected agrochemicals and heavy metals, and Leptospira. Water samples at the worksite will be collected and measured for nephrotoxic agrochemicals and heavy metals at the three collection time points. Results of this research will lead to large-scale intervention trials that will help to prevent CKDu in vulnerable populations, and to the broad dissemination of results internationally.